The present invention relates to a conveyor system for transporting articles, in particular containers for baggage pieces. The present invention further relates to a control method for such a conveyor system.
It is known to use conveyors for transporting articles, such as baggage pieces, for example at airports. One or more baggage pieces are, for example, placed in a suitable container. The conveyor, which is typically understood to include a conveying element with a drive, a conveyor belt, cross members, etc., is here composed of several conveyer sections, each of which includes an endless conveyor belt and a drive motor. The conveyor sections are connected sequentially in such a way that the conveyor belts transfer the containers that are transported by the conveyor belts in the transport direction, so as to enable the baggage pieces in the containers to be transported from a start position to a target position. In addition, the conveyor can also serve as an intermediate storage unit for the baggage pieces. A baggage piece deposited the evening before departure date can travel continuously in a circle during the night. The conveyor deposits the baggage pieces at the target position only shortly before the scheduled departure time for subsequent loading onto the aircraft.
The transport speed of the conveyor sections thereby depends on the transported articles. The different transport speeds reduce the capacity of the intermediate storage unit and make data tracking and/or handling of an individual item difficult.
To improve this situation, the conveyor belts in a conveyor section are either shortened so as to transport as a smaller number of articles on the conveyor belt, or controlled drives with a feedback of the rotation speed are employed. Servo motors with a stabilized rotation speed can also be used. Conveyors of this type are relatively expensive.
FIG. 3 shows a conventional conveyor system 1 including an upstream conveyor 2 and a downstream conveyor 3 at various points in time t1 to t9. The transport direction is indicated by the arrow 4. In the schematic illustration of FIG. 3, the conveyor 2 is depicted by a conveyor belt 6, whereas the conveyor 3 is depicted by the conveyor belt 7. Articles 5, transported on a conveyor belt 6, 7 and placed on conveyor sections, are also indicated schematically by black boxes. The articles 5 can be separate baggage pieces or containers that hold one or several baggage pieces. Each conveyor belt 6, 7 is here driven by an unregulated, uncontrolled, load-torque-dependent asynchronous motor (not shown) with a fixed, unchangeable desired rotation speed nsoll.
The process starts at time t1, when nine evenly distributed articles 5 are transported from the conveyor belt 6 in the transport direction 4 to the downstream conveyor belt 7. Because the actual rotation speed nist(t) of the asynchronous motor depends on the load torque, the speeds of the conveyor belts 6, 7 at time t1 are different. In other words, the empty conveyor belt 7 runs faster than the conveyor belt 6 which carries the weight of the nine articles 5. At time t2, the first article 8 in the transport direction 4 is transferred to the downstream conveyor belt 7, so that at time t2, eight articles 5 are transported on the first conveyor belt 6. The actual rotation speed nist(t) of the asynchronous motor and hence also the actual transport speed vist(t) of the conveyor belt 7 is reduced relative to the actual rotation/transport speed at time t1 due to the weight of the first article 8. Consequently, the actual rotation speed nist(t) of the asynchronous motor and hence also the actual transport speed vist(t) of the conveyor belt 6 have increased relative to the corresponding rotation/transport speed at time t1, since only eight articles 5 are transported.
At time t3, the conveyor belt 7 transports two articles 5 and the conveyor belt 6 seven articles 5. The actual transport speed vist(t) of the conveyor belt 6 increases further relative to the transport speed at time t2, whereas the actual transport speed vist(t) of the downstream conveyor belt 7 is further reduced since it received the second article 9. Due to the change in the actual transport speed vist(t) of the conveyor belt 7 from the time t2 to the time t3, the first article 8 has been transported at a faster pace by the conveyor belt 6 than the second article 9. As a result, the resulting spacing 10 between the first article 8 and the second article 9 on the conveyor belt 7 is greater than the spacing that existed between the first article 8 and the second article 9 at the time t1 on the conveyor belt 6.
After the transfer of the third article 11, as seen in the transport direction 4 from the conveyor belt 6 to the conveyor belt 7, the actual transport speed vist(t) of the conveyor belt 6 again increases, whereas the trailing conveyor belt 7 again slows down. As a result, the spacing between the second article 9 and the third article 11 is smaller than the spacing 10.
At time t5, the actual transport speed vist(t) of the conveyor belt 6 is approximately equal to the actual transport speed of the conveyor belt 7. At the times t6, t7, t8, t9, the actual transport speed vist(t) of the conveyor belt 6 increases from one point in time to the next, while the actual transport speed vist(t) of the conveyor belt 7 decreases accordingly, so that two articles 5 collide with each other on the conveyor belt 7, as illustrated for the time t9.
It would be desirable and advantageous to provide a more cost-effective conveyor belt system and a method for operating such conveyor belt system which obviates prior art shortcomings and is able to provide a constant throughput and also function as an intermediate storage unit.